On Sunday, if all goes well, Space Exploration Technologies, or SpaceX, will achieve a spaceflight first.

After delivering cargo to the International Space Station, the first stage of the Falcon 9 rocket used for the flight will fire its engines for the second time. The burn will allow the rocket to reenter the atmosphere in controlled flight, without breaking up and disintegrating on the way down as most booster rockets do.

The machine will settle over the Atlantic Ocean off the coast of its Cape Canaveral launchpad, engines roaring, and four landing legs will unfold from the rocket’s sides. Hovering over ocean, the rocket will kick up a salt spray along with the flames and smoke. Finally, the engines will cut off and the rocket will drop the last few feet into the ocean for recovery by a waiting barge.

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